Genomic organization of the complex α-gliadin gene loci in wheat
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To better understand the molecular evolution of the large α-gliadin gene family, a half-million bacterial artificial chromosome (BAC) library clones from tetraploid durum wheat, Triticum turgidum ssp. durum (2n=4x=28, genome AB), were screened for large genomic segments carrying the α-gliadin genes of the Gli-2 loci on the group 6 homoeologous chromosomes. The resulting 220 positive BAC clones—each containing between one and four copies of α-gliadin sequences—were fingerprinted for contig assembly to produce contiguous chromosomal regions covering the Gli-2 loci. While contigs consisting of as many as 21 BAC clones and containing up to 17 α-gliadin genes were formed, many BAC clones remained as singletons. The accuracy of the order of BAC clones in the contigs was verified by Southern hybridization analysis of the BAC fingerprints using an α-gliadin probe. These results indicate that α-gliadin genes are not evenly dispersed in the Gli-2 locus regions. Hybridization of these BACs with probes for long terminal repeat retrotransposons was used to determine the abundance and distribution of repetitive DNA in this region. Sequencing of BAC ends indicated that 70% of the sequences were significantly similar to different classes of retrotransposons, suggesting that these elements are abundant in this region. Several mechanisms underlying the dynamic evolution of the Gli-2 loci are discussed.
The authors thank Dr. Frances M. Dupont for reading the manuscript and making suggestions and corrections. All experiments comply with US laws.
- Clarke BC, Appel R (1999) Sequence variation at the Sec-1 locus of rye, Secale cereale (Poaceae). Pl Syst Evol 214:1–14Google Scholar
- D’Ovidio R, Lafiandra D, Tanzarella OA, Anderson OA, Greene FC (1991) Molecular characterization of bread wheat mutants lacking the entire cluster of chromosome 6A-controlled gliadin components. J Cereal Sci 14:125–129Google Scholar
- D’Ovidio R, Tanzarella O, Masci S, Lafiandra D, Porceddu E (1992) RFLP and PCR analyses at Gli-1, Gli-2, Glu-1 and Glu-3 loci in cultivated and wild wheats. Hereditas 116:79–85Google Scholar
- Herberd NP, Bartels D, Thompson RD (1985) Analysis of the gliadin multigene loci in bread wheat using nullisomic–tetrasomic lines. Mol Gen Genet 198:234–242Google Scholar
- Herberd NP, Flavell RB, Thompson RD (1987) Identification of a transposon-like insertion in a Glu-1 allele of wheat. Mol Genet Genomics 209:326–332Google Scholar
- Huang S, Sirikhachornkit A, Su X, Faris J, Gill B, Haselkorn R, Gornicki P (2002) Genes encoding plastid acetyl-CoA caroxylase and 3-phosphoglycerate kinae of the Triticum/Aegilops complex and the evolutionary history of polyploid wheat. Proc Natl Acad Sci USA 99:8133–8138CrossRefPubMedGoogle Scholar
- Joppa LR, Du C, Hart GE, Hareland GA (1997) Mapping a QTL for grain protein in tetraploid wheat (Triticum turgidum) using a population of recombinant inbred chromosome lines. Crop Sci 37:1586–1589Google Scholar
- Khan IA, Procunier JD, Humphreys DG, Tranquilli G, Schlatter AR, Marcucci-Poltri S, Fronhberg R, Dubcovsky J (2000) Development of PCR-based markers for a high grain protein content gene from Triticum turgidum ssp. dicoccoides transferred to bread wheat. Crop Sci 40:518–524Google Scholar
- Lafiandra D, Kasards DD, Morris R (1984) Chromosomal assignment of genes coding for the wheat gliadin protein components of the cultivars Cheyenne and Chinese Spring by two-dimensional (two-pH) electrophoresis. Theor Appl Genet 68:531–539 Google Scholar
- Payne PI (1987) Genetics of wheat storage proteins and the effect of allelic variation on breadmaking quality. Annu Rev Genet 38:141–153Google Scholar
- Shewry PR, Tatham AS, Kasarda DD (1992) Cereal proteins and coeliac disease. In: Marsh MN (ed) Coeliac disease. Blackwell, London, pp 305–348Google Scholar
- Wei F, Wing RA, Wise RP (2002) Genome dynamics and evolution of the Mla (powdery mildew) resistance locus in barley. Plant Cell 14:1903–1917Google Scholar